The present invention relates to an apparatus and method for the identification of assisted and unassisted heart beats during intra-aortic balloon pump assistance, and in addition, to a means for determining the true arterial systolic and diastolic pressures during intra-aortic balloon pump assistance.
The intra-aortic balloon pump ("IABP") is used as a means of temporary mechanical support of the left ventricle to treat several forms of heart disease. During IABP support, clinicians are guided for assessment of patient conditions by monitoring various cardiac parameters including arterial pressure, cardiac index, pulmonary artery wedge pressure and pulmonary capillary wedge pressure. The monitoring of these cardiac parameters is also important for the weaning of the heart from IABP support. The measurement of arterial pressure is affected by IABP support and can thus provide misleading information as to the true condition of an individual's heart.
Arterial blood pressure measurement, for example, is used to determine the diastolic pressure (low pressure) and the systolic pressure (high pressure) of the heart. Existing methods of monitoring arterial pressure identify the diastolic and systolic pressures as the minima and maxima of the arterial pressure waveform. However, during IABP support the inflation and deflation of the intra-aortic balloon in the descending thoracic aorta during diastole creates an extra beat on the arterial blood pressure waveform next to the heart beat in the same cardiac cycle. The existing cardiovascular monitoring systems do not distinguish between the heart beat and the balloon beat during IABP support, and as a result, these monitoring systems average the high pressure of the balloon with the systolic pressure of a patient's heart, and average the dicrotic notch with the diastolic pressure of a patient's heart. This averaging results in the determination of erroneous values for arterial systolic and diastolic pressures, and thus the condition of a patient's heart is not accurately monitored.
Several types of artifact rejection methods have been described for use in determining true blood pressure values. One such approach uses sphygmometric blood pressure monitoring (see, for example, U.S. Pat. Nos. 4,174,707 and 4,777,959) and another approach uses the recognition and discrimination amongst Korotokoff sounds in the measurement of blood pressure to reject artifacts and to determine minimum and maximum pressures (see, for example, U.S. Pat. No. 4,867,171). One blood pressure detection method has been developed for use during intra-aortic balloon pump assist to separate heart beats from balloon beats: however this method requires the R--R interval values and QRS timing from an ECG beat detector in order to determine whether an arterial blood pressure beat is a balloon beat or a heart beat (Elghazzawi et al., 1991, Jour. of Clinical Monitoring, Vol. 7, pp. 97-98).
It is the purpose of the present invention to overcome the aforementioned difficulties in monitoring the condition of a patient's heart, and to provide a physician with accurate information to be used in assessing the progress of a patient's recovery.